Insulator tester



Aug. 6, E1929. T. lssHlKl 1,723,861

' INSULATOR TESTER Filed July 13, 1925 2 Sheets-sheer 1 HATE CURRENT Inventory Teizo lshm,

His Attorrweg.

l Allg. 6, 1929. T |55H|K| 1,723,861

INSULATOR TESTER Filed July 13, 1925 2 Sheets-Sheet 2 A Fi .5.

6 A /3 gy@ /4 /Z ZZ ,5 /a T/Z 22 l rfi rf rf* Inventor Teizo IsshK, y b9 His Attorney.

Patented Aug. 6, 1929.

UNITED STATES TEIZO ISSHIKI, OF TOKYO, JAPAN, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A

CORPORATION OF NEW YORK.

INSULAYTOB TESTER.

Application. mea my 1s, :925, serial No.

I My invention relates to apparatus for testing insulators while they are in use and has for its object a portable tester which is compact, accurate and reliable.

In carrying my invention into effect I employ apparatus which utilizes the static voltage existing on the insulator while in use. A suitable contact pole upon which is mounted a condenser is used to connect the insulator to be tested to ground through such condenser. A portion of the static voltage across the condenser is applied to the grid of a vacuum tube detector and a measuring instrument or other curre'nt detector is connected in the plate circuit of the tube. In certain cases amplification of the detecting current may be desirable. The apparatus is preferably made up in portable form so that it may easily be carried about for field use.

The features of my invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. For a better understanding of my invention, reference is made in the following description to the accompanying drawing; in which Fig. 1 is a connection diagram of a device embodying my invention; Fig. 2 is an enlarged cross-sectional plan view of the contact pole taken on theline 2 2 of Fig. l; Figs. 3 and 4 represent curves showing the lrelation between the grid-voltage and plate current of the vacuum tube detectingI apparatus; and Figs. 5 and 6 are connection diagrams respectively where vamplifiers are used. vThe same reference numerals represent the same or similar portions throughout the drawing.

Now referring to Fig. 1 which is :an embodiment of my invention, the contact pole is provided with a handle of non-conducting material 1 with an insulator 2 at its end and a contact piece 3 fitted into the top ofthe insulator 2. A metallic induction plate 4 is fitted on a part of the insulator surface along its circumference and another metallic induction plate 6 is placed around the external periphery and separated from plate 4 by an lnsulating layer 5, thus constitutin a condenser. To the induction plates escribed above are connected the conductors 7 and 8 respectively. A suiiicient dielectric strength should be maintained between the'contact piece 3 and the induction plates to guard against the working voltage of the transmis.- sion line. and it is preferable to have the 43,108, yand in Japan November 1o, 1924.

conductor 7 insulated, or otherwise protected from static effects of any body other than the tween the contact point and earth, and a voltage4 will'be statically induced between the induction plates. The amount of the voltage between the induction plates will be equal to the product of the voltage between the contact point and ground and the ratio of electric capacity between the contact piece and induction plate 6 and the electric capacity between both induction plates. This voltage is proportional to the voltage between the contact point and ground, and may be altered by changing the relative spacing of contact piece 3, plate 4 and plate 6. 11 and 12 are variable condensers which operate to reduce the voltage between the terminals 9 and 10 of conductors 7 and 8 if desired vand to apply it to the grid of a three electrode vacuum tube 15.- 13 and 14 are leakage resistances for said condensers and are used only when lthey are necessary. The three electrode vacuum tube 15 can be regulated by a suitable adjustment of plate potential, filament current and negative grid bias potential VG, so that when there is no voltage between terminals 10 and 9, the conditions of the tube will correspond to point P of Fig. 3 that is the plate current is of about zero value. When the alternating current voltage induced between terminals 9 and 10 is 4suitably stepped down to Vc' and is impressed on the grid of the vacuum tube, the current corresponding to OP of Fig. 3 will flow in the plate circuit during the half cycle in which said voltage is positive with respectto the filament, and no current will flow through the plate circuit in the negative half cycle. Accordingly direct current ammeter 16 in the plate circuit will indicate the average value of the currentl OP flowing during positive half cycles, which value is a function of Vz, and 1s proportional to the induced voltage between the induction plates 4 and 6. Now, by adjusting the voltage VG produced by the battery 21 so' that the maximum value of Vc' will not surpass the'grid biasing voltage VG, a plate current corresponding to Vi will ow, but without any iiow of grid current, whereby the induced voltage between terminals 9 and 10' out the indication of the ammeter and then compare it with the indication obtained by bringing the tip contact 3 to the connection 18 `above the first section 19 of the insulator string. Since the indication of ammeter 16 obtained from the transmission line Corresponds yto 4the voltage between the transmission line and earth, the voltage at point 18 should be considerably below that at point 17 if the first section is sound, while if it is defective the difference will be very small and thus detected at once. In this procedure it is necessary to measure the indication of the ammeter previously on a perfect insulator, and a certain standard obtainedfor the purpose of judgment. rIhen the tip of contact piece 3 should be shifted to the point Q0 and the same procedure repeated.

If the current in the plate circuit of the three electrode Vacuum tube is small the current canl be amplified by using three electrode vacuum amplifier 15 as shown in Fig. 5 'or by amplifying in'. several steps, such for instance as three steps as shown in Fig. 6; in these figures the transformer connections between the tubes are representative of one of several possible connections. AIn such cases the grid potential of the first4 three electrode vacuum tubes need not be' so adjusted, when Y there is no voltage between terminalsv9 and 10, that it corresponds to the point P of Fig. 3, that is, its plate current need not be Zero, but it is preferable to be adjusted to correspond with the point Q, Fig. 4. The grid voltage of the last amplifier may then be so adjusted that it corresponds with the point P Vof Fig. 3 when the ain-meter 16 is directly inserted in the plate circuit. The ammeter may be connected through a transformer 22 as indicated at the right of Figs. 5 and 6 in which case the last amplifier may be adjusted to correspond to point Q of Fig. 4. In the formercase the ammeter may be either a direct current or an alternating current instrument and in the latter case it must be an alternating current instrument. Any other vtype of current detector may be employed in place of an ammeter. v

In accordance with the provisions of Ythe Patent Statutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it under stood that the apparatus shown and described is only illustrative and that the invention may be carried out by other means.

What I claim as new and ldesire-to secure by Letters Patent of the United States, is:

1. Apparatus for testing insulators comprising a multiple plate condenser arranged to be connected between the insulator to be tested and ground, a three-electrode vacuum tube having grid and plate circuits, a current detector for detecting the flow of current in the plate circuit of said tube, and variable condenser apparatus connected in. parallel with a portion of said first mentioned condenser for applying an adjustable voltage proportional to the static voltage of said in'- sulator to the grid of said tube.

2. -A portable insulator testing apparat-us comprising a multi-plate condenser mounted lupon a pole and having terminals for conpole of non-conducting material, a cylindrical insulator on one end of said pole, a contact rod embedded in said insulator and extending therefrom in an axial direction, a metallic plate along one circumference of said insulator, and a cylindrical conductor surroundlng said parts and separated from said plate by a layer of insulation, said parts forming a three-plate condenser from which a static voltage less than but proportional to a static voltage charge between said contact rod and cylindricalI conductor may be obtained.

In witness whereof, I have hereunto set my hand this twentieth day of June, 1925.

TEIzo vISSHIKI.

3. In apparat-us for testing insulators, a 

